1. Field of the Invention
The present invention relates to a camera system having a data communicator function between a camera body and a photographing lens.
2. Description of Related Art
In a recent single lens reflex camera having an automatic focusing device, information peculiar to a photographing lens, such as open F-number data used in an automatic exposure function or an automatic focusing function is sent as electrical signals from the photographing lens to a CPU (central processing unit) of a camera body.
Information peculiar to the photographing lens is stored in a lens ROM provided in the photographing lens. The photographing lens and the camera body are provided with electrical contacts on a lens mount and a body mount to transmit and receive signal information between the photographing lens and the camera body, respectively. The body CPU transmits and receives signal information to and from the lens ROM through the electrical contacts and reads the data stored in the lens ROM. A clock pulse is output from the camera body to send address signals from the body CPU synchronously therewith, so that predetermined data can be output from the lens ROM in accordance with the address signals.
Furthermore, in a single lens reflex camera having a photographing lens with an AF motor (automatic focusing motor) and a PZ motor (power zoom motor), etc., if control of the motors is effected by the body CPU, there will be an over load on the body CPU. In particular, in a single lens reflex camera in which various kinds of photographing lenses are exchangeably mounted to one camera body, the body CPU must read different parameters depending on the photographing lenses from the associated lens ROM's and perform predetermined arithmetic operations in accordance with the read parameters to control the photographing lenses. This makes quick operations impossible or next to impossible.
In addition to the foregoing, various data, is stored in the ROM of the photographing lens. In particular, in a zoom lens in which a zoom code plate, which comes into sliding contact with brushes provided on a zoom ring when a latter is rotated, has focal length values corresponding to the divided codes of the zoom code plate, the respective focal length values are stored separately in the ROM of the photographing lens. Accordingly, the ROM has to have a large capacity memory. It is necessary to erase the stored necessary data or to troublesomely replace the ROM with a larger capacity ROM in order to write new data therein.